This research will investigate the arrangement and function of DNA sequences from the eukaryote, D. melanogaster. Our approach is to intensively examine the arrangement in a few regions. The first region contains the DNA in and around the rosy gene. This gene codes for xanthine dehydrogenase. It was selected for our study because it has been and can continue to be studied by high resolution genetics. These genetic studies offer the possibility of identifying the function of the DNA sequences we examine. The gene is to be isolated from a set of bacteria that contain in vitro recombinants between bacterial plasmids and D. melanogaster DNA. We have isolated a recombinant molecule that maps near the rosy locus. Through a series of molecular hybridization screens of our set of recombinants, we propose to walk to the rosy gene over a series of overlapping DNA molecules. When we arrive at the gene we will use standard techniques to locate repeated and palindromic sequences as well as the sequences complementary to mRNA and hnRNA. The other regions to be studied contain clusters of middle repetitive DNA with interspersed non-repetitive and transcribed DNA. Once again, using standard techniques we will examine the arrangement of these repetitive sequences relative to the regions that are palindromic and those that are transcribed.